The invention relates to a heat-sealable barrier laminate structure which produces an oxygen impermeable, leak free container. More particularly, this invention relates to barrier laminate structures which are comprised of specific high strength polymer resin layers which effectively prevent heat activation pinholes, cuts or cracking of oxygen barrier layers caused during scoring and especially during folding and heat sealing of the laminate in package formation.
The invention as disclosed and claimed herein is closely related to pending application Ser. Nos. 191,987; 191,988 now U.S. Pat. No. 4,888,222; 191,989 now U.S. Pat. No. 4,880,701; 191,992 and 191,337 now U.S. Pat. No. 4,859,513, all owned by the Assignee. Also, application Ser. Nos. 354,570 and 354,591 have been concurrently filed and are related. Thirdly, structures for paperboard containers using heat-sealable polymer resins and containing various oxygen barrier materials are disclosed in U.S. Pat. Nos. 3,972,467; 4,698,246; 4,701,360; 4,789,575 and 4,806,399, all owned by the Assignee.
Heat-sealable low density polyethylenes are well known to be components of current paperboard food and/or non-food packages which provide little barrier to the transmission of oxygen. Pinholes, cuts, score line cracks or channels, existent in conventional packaging and cartons, create additional leakage sites. It is well known that impermeable materials such as aluminum foil, polar brittle materials such as: polyacrylonitriles, polyvinylidene chlorides, polyvinyl chlorides, etc., provide varying degrees of barrier to the transfer of oxygen. However, all these materials lack the requisite strength at high rates of deformation, namely stress cracking resistance during scoring, package formation and distribution abuse to provide a resultant oxygen impermeable and airtight structure. In addition, leakage through the uncaulked channels of the carton in the top, bottom and side seam have likewise resulted in poor whole carton oxygen barrier properties.
The existing commercial structures for a paperboard carton for liquid and solid, food and non-food, products have utilized an easily heat-sealable barrier laminate composed of a paperboard substrate and a foil oxygen barrier layer, both being sandwiched between two thick layers of low density polyethylene (LDPE). The LDPE is a relatively inexpensive heat-sealable moisture barrier material. The conventional structure falters in that the foil layer which acts as the barrier to the transmission of oxygen in and out of the carton cracks during blank conversion, carton formation, and package distribution stages.
Bending and folding occurring during the formation of a gable "type" top, flat "type" top, or other folded, heat-sealed top closure, and a fin-sealed, or other conventional folded bottom puts excessive amounts of local stress on the thin foil and/or other oxygen barrier layer and, as typically results, cracks and pinholes appear.
To date, there have been no economically attractive commercially available paperboard packages which consistently approach the oxygen impermeability of glass or metal containers. The object of the present invention is to produce an oxygen impermeable, leak free container and/or laminate structure such as a paperboard based package or carton that prevents the transmission of gases therethrough, and in addition, prevents the escape of flavor components or the ingress of contaminates. A further object of the present invention is to produce such a package that is economical on a per-package cost basis, is fundamentally compatible with existing converting machinery and can be formed, filled and sealed at economically high speeds using conventional packaging machine temperatures, pressures and dwell times.
Another object of the present invention is to provide this oxygen impermeable package in a variety of applications including four-ounce to 128-ounce containers, or larger, as required by the packager.
A further object of this invention is to incorporate a functional polymer layer which exhibits high strength, abuse resistance and toughness during converting and carton forming in combination with aluminum foil or other oxygen barrier layers and paper, paperboard or other mechanically stable structural material such that the high-strength layer reduces the stresses incurred by the barrier layers during blank conversion, package formation, and distribution. Additionally, should a penetration of the barrier layer or layers occur, the high-strength layer serves to maintain package integrity at the failure site. The high-strength, heat-resistant layer effectively prevents heat activation pinholes through the product contact layer, even when non-foil barrier layers are used.